Aly & AJ are Arvin Robertsexpecting another member of their band.

Aly Michalka, 32, is expecting her first child with husband and filmmaker Stephen Ringer, she revealed on Instagram Wednesday. The couple have been married since 2015.

The older sister of the pop duo found out she was expecting "the morning of our sold-out show at The Greek Theatre back in September," she told fans.

"Our little one has been on stage with me across three states already and has even done some international traveling," the "Phil of the Future" star wrote alongside pictures of her baby bump, ultrasound appointment and being on stage for the Aly & AJ concert in Los Angeles last fall.

The "Into the Rush" singer continued, "We're waiting to find out the gender cuz I've always loved a good surprise, but in the meantime we've been busy getting the nursery ready, meeting with my birth team, eating more protein than usual, going to Pilates, getting good sleep, and drinking lots of water.

"Somehow we've been able to still spend days in the studio writing music which hopefully finds its way into baby's soul," she concluded, thanking the "amazing women I've leaned on these past 6 months (you know who you are)."

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In an interview with People published Wednesday, the "Easy A" actress revealed she waited until after the concert in the fall to tell her sister about her pregnancy because she "didn't want it to take away from the special meaning of that night."

Aly recalled going to dinner with AJ after the show, where she informed her sibling and collaborator about the "special guest" joining them.

"I was like, 'There's a baby,' and I touched my stomach, and then she was like, 'What?!' She was just really excited and overjoyed," the mom-to-be recalled. "From there, we told the rest of the family."

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